Electric motor-driven compressor having bi-directional liquid coolant passage

ABSTRACT

An electric motor-driven compressor includes a motor having a rotor and a stator in a motor housing, a low-pressure compressor mounted to one end of the motor housing, and a high-pressure compressor mounted to the other end of the motor housing, the compressors forming a two-stage compressor. The motor housing defines a convoluted liquid coolant passage having a plurality of axially spaced-apart, convoluted passageways arranged for serial flow of liquid coolant from the passage inlet, then through each of the convoluted passageways one after another, and finally out from the outlet. The coolant passage further defines at least a first bypass passage that intersects with the convoluted passageways and extends in a non-convoluted fashion so as to interconnect the convoluted passageways and provide an alternative flow path for the coolant.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is related to commonly owned, co-pending application Ser. No. 14/184,122 filed on Feb. 19, 2014 and Ser. No. 14/226,309 filed on Mar. 26, 2014, the entire disclosures of which are hereby incorporated herein by reference.

BACKGROUND

The present disclosure relates to electric motor-driven compressors such as used for fuel cells.

Air compressors can be used to increase the efficiency of a fuel cell by providing compressed air to the cathode side of the fuel cell. A two-stage compressor may be used in some applications requiring a higher pressure than achievable in a single compressor stage. In a two-stage compressor, a low-pressure compressor wheel is provided on a shaft, and a high-pressure compressor wheel is provided on the same shaft. The shaft is driven by an electric motor so that the compressor wheels are rotated, and air enters the low-pressure compressor wheel and is compressed to a first pressure. The compressed air is then passed on to the high-pressure wheel for a further increase in pressure. The air from the high-pressure compressor wheel is then delivered to the fuel cell to promote the fuel cell reaction.

The electric motor used in a compressor for a fuel cell is typically a high-speed, high-output motor that generates a significant amount of heat. Additionally, the air compression process also generates heat. It is necessary to provide effective heat transfer away from the electric motor-driven compressor, such as by circulating a liquid coolant around the motor components.

BRIEF SUMMARY OF THE DISCLOSURE

The present disclosure describes embodiments of electric motor-driven compressors such as useful with fuel cells or in other applications. In one embodiment, for example, an electric motor-driven compressor includes a housing assembly comprising a motor housing and a compressor housing mounted to the motor housing. The motor housing contains a motor stator and a motor rotor, and defines a bore through which a rotatable shaft passes. The compressor housing contains a centrifugal compressor wheel that is mounted on the shaft for rotation about the shaft axis. The compressor housing also defines an air inlet that leads air into the compressor wheel, and a volute that collects compressed air that has passed through the compressor wheel.

In accordance with the present disclosure, the motor housing defines a liquid coolant passage for circulating a liquid coolant. The configuration of the coolant passage is a particular focus of the present disclosure, and in the illustrated embodiment described herein the coolant passage is a convoluted liquid coolant passage. The coolant passage defines an inlet and an outlet respectively located proximate opposite ends of the motor housing, and defines a plurality of axially spaced-apart, convoluted passageways arranged for serial flow of liquid coolant from the inlet, then through each of the convoluted passageways one after another, and finally out from the outlet.

In one embodiment the coolant passage further defines at least a first bypass passage that intersects with the convoluted passageways and extends in a non-convoluted fashion so as to interconnect the convoluted passageways and provide an alternative flow path for some of the liquid coolant from the inlet to the outlet.

The coolant passage can further define a second bypass passage that intersects with the convoluted passageways and extends in a non-convoluted fashion so as to interconnect the convoluted passageways, the first and second bypass passages being circumferentially spaced apart from each other.

The features of the present invention can be applied to a two-stage serial compressor, such as the embodiment illustrated and described herein. In the case of such a two-stage compressor, a second compressor housing is mounted to an opposite end of the motor housing and a second centrifugal compressor wheel is contained in the second compressor housing and is affixed to an opposite end of the shaft. The second compressor housing defines a second compressor flow path including a second air inlet that leads air into the second compressor wheel, and a second volute that collects compressed air that has passed through and been compressed by the second compressor wheel. An interstage duct connects the second volute to the first air inlet such that air compressed by the second compressor wheel is led by the interstage duct from the second volute into the first air inlet and is further compressed by the first compressor wheel and delivered into the first volute. The second compressor wheel thus constitutes a low-pressure compressor wheel and the first compressor wheel constitutes a high-pressure compressor wheel.

The inlet to the coolant passage advantageously is proximate the high-pressure compressor wheel and the outlet from the coolant passage is proximate the low-pressure compressor wheel.

In the embodiment described herein, the convoluted passageway proximate the high-pressure compressor wheel has a larger cross-sectional area than the convoluted passageway proximate the low-pressure compressor wheel.

The electric motor-driven compressor can further include a heat shield disposed between the motor housing and the first compressor housing, and the heat shield can define a mounting flange captured between the motor housing and the first compressor housing. The mounting flange is in contact with a portion of the motor housing cooled by the coolant passage so as to facilitate heat transfer from the mounting flange to said portion of the motor housing.

In one embodiment, a heat-conducting material is disposed between the motor stator and the motor housing such that the heat-conducting material is in contact with both the motor stator and the motor housing and serves as a thermally conductive pathway from the motor stator to the motor housing. This enhances heat transfer away from the stator and into the liquid coolant. The heat-conducting material can be, for example, a heat-conducting epoxy.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described the present disclosure in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

FIG. 1 is a side view, partly in section, of an electric motor-driven compressor in accordance with one embodiment of the invention, comprising a two-stage compressor having a low-pressure compressor and a high-pressure compressor in series;

FIG. 2 is a perspective view of a coolant core used in the casting of the motor housing in FIG. 1, which core dictates the configuration of the liquid coolant passage in the motor housing;

FIG. 3 is another perspective view of the coolant core; and

FIG. 4 is yet another perspective view of the coolant core.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention now will be described more fully hereinafter with reference to the accompanying drawings in which some but not all embodiments of the invention are shown. Indeed, aspects of the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

The present invention may be applied in a variety of types of electric motor-driven compressors, including single-stage as well as multi-stage electric motor-driven compressors. The particular embodiment described herein for purposes of explaining the principles of the invention is a serial two-stage compressor having two centrifugal compressors arranged in series, but the invention is applicable to parallel two-stage compressors as well as other types. Thus, a simplified cross-sectional view of a serial two-stage electric motor-driven compressor 10 for use with a fuel cell (such as a proton exchange membrane (PEM) fuel cell) is shown in FIG. 1. The two-stage compressor 10 includes a housing assembly comprising a motor housing 20, a low-pressure compressor housing 40 mounted to one end of the motor housing, and a high-pressure compressor housing 60 mounted to the other end of the motor housing. The motor housing 20 contains a motor stator 22 and a motor rotor 24 having a shaft 26 about which permanent magnets 28 are fixedly mounted. The motor housing 20 defines a bore 30 through which the motor rotor 24 and the shaft 26 pass. Air journal bearings 32 are disposed in the motor housing 20 for rotatably supporting the rotor 24 and shaft 26. The low-pressure side journal air bearings 32 are retained in a separate bearing housing 39 disposed between the motor housing 20 and the low-pressure compressor housing 40.

The low-pressure compressor housing 40 contains a centrifugal low-pressure compressor wheel 42 that is mounted on one end of the shaft 26 for rotation therewith, the low-pressure compressor housing also defining a low-pressure compressor flow path including an air inlet 44 that leads air into the low-pressure compressor wheel, and a low-pressure volute 46 that collects compressed air that has passed through and been compressed by the low-pressure compressor wheel. The low-pressure compressor also includes a diffuser 45 that leads the compressed air from the low-pressure compressor wheel 42 into the low-pressure volute 46, and serves to reduce the velocity and increase the static pressure of the air going into the volute.

The high-pressure compressor housing 60 contains a centrifugal high-pressure compressor wheel 62 that is mounted on the opposite end of the shaft 26 for rotation therewith. The high-pressure compressor housing defines a high-pressure compressor flow path including an air inlet 64 that leads air into the high-pressure compressor wheel, and a high-pressure volute 66 that collects compressed air that has passed through and been compressed by the high-pressure compressor wheel. The high-pressure compressor also includes a diffuser 65 that leads the compressed air from the high-pressure compressor wheel 62 into the high-pressure volute 66, and serves to reduce the velocity and increase the static pressure of the air going into the volute.

The compressor further includes an interstage duct 50 that is connected between the low-pressure volute 46 and the inlet 64 to the high-pressure compressor for routing the compressed air from the low-pressure volute 46 to the high-pressure compressor for further pressurizing in a second-stage compression process.

Cooling air passages are defined in the housing assembly for supplying cooling air to the air bearings 32. In particular, cooling air is supplied into a cooling air supply inlet (not shown) defined in the motor housing 20. For example, in the case of the compressor 10 being used in a fuel cell system for a vehicle, where the compressed air from the high-pressure volute 66 is passed through a vehicle heat exchanger to cool the air before it is supplied to the fuel cell, a portion of the air exiting the heat exchanger can be tapped off and supplied into the cooling air supply inlet. From there, the cooling air passes into an annulus 72 defined cooperatively by the motor housing 20 and the bearing housing 39. A portion of the cooling air in the annulus 72 is directed radially inwardly through passage 73 defined in the bearing housing 39 and is fed to both sides of a thrust plate 43 for the low-pressure side air thrust bearing. The air on the inboard (motor) side of the thrust plate 43 feeds the journal air bearing 32 (also cooling the rotor magnet 28) and is then discharged into the motor cavity. The air on the outboard side of the thrust plate 43 proceeds radially outwardly through passages 47 into an annular space 49 defined in the compressor housing, and from there it proceeds through a passage 51 into the motor cavity.

The remainder of the cooling air in the annulus 72 is directed through an axially extending cooling air conduit (not shown) that extends from the annulus 72 through the motor housing 20 and connects with a further annulus 76 in the region of the high-pressure compressor. The motor housing 20 defines cooling air passages 78 that lead from the annulus 76 generally radially inwardly into a generally annular space 80 at the high-pressure end of the motor rotor 24. Cooling air fed into the generally annular space 80 passes generally axially (to the left in FIG. 1) and feeds the journal air bearing 32 for the rotor 24 (also cooling the rotor magnet 28) and is then discharged into the motor cavity.

The cooling air in the motor cavity is evacuated from the motor cavity via a port (not shown).

The high-pressure compressor includes a generally annular heat shield 100 that is formed separately from the high-pressure compressor housing 60 and the motor housing 20 and is disposed therebetween. In particular, the heat shield 100 has a flange 102 at its radially outer periphery, and the flange 102 is disposed, with respect to the radial direction, between a flange 68 of the compressor housing 60 and a shoulder 21 of the motor housing 20, and is sandwiched between the flange 68 and shoulder 21 so as to constrain the heat shield radially. The heat shield flange 102 is captured and constrained axially between a motor housing flange 23 and a shoulder on the HP compressor housing 60. A V-band clamp 35 clamps together the motor housing flange 23 and HP compressor housing flange 68, and a sealing ring disposed between the HP compressor housing shoulder and the heat shield flange 102 is thereby axially compressed between these parts, thereby sealing the interface between the heat shield and the compressor housing. The heat shield 100 includes a radially directed wall portion 104 that extends radially inwardly from the flange 102 and defines one wall of the diffuser 65 for the compressed air delivered into the HP volute 66, an opposite wall of the diffuser being defined by the HP compressor housing 60.

With continued reference to FIG. 1, the previously described cooling air annulus 76 is defined cooperatively by the heat shield 100 and the motor housing 20. The cooling air passages 78 in the motor housing extend from the annulus 76 radially inwardly and feed the cooling air into the space 80 from which the air feeds the journal bearing as previously described. Thus, the heat shield 100 cooperates with the housing assembly to define part of the cooling air passages for the cooling air supplied to the air bearings.

The heat shield 100 also helps minimize heat transfer from the hot motor housing 20 to the air passing through the high-pressure compressor. To this end, the motor housing 20 makes little contact with the heat shield 100. The motor housing 20 defines a liquid coolant passage 25 for circulating a liquid coolant through the housing around the stator 22. The heat shield's mounting flange 102 captured between the motor housing 20 and the HP compressor housing 60 is in contact with a portion of the motor housing cooled by the liquid coolant in the liquid coolant passage 25 (note the close proximity of the flange 102 to the coolant passage 25 in FIG. 1) so as to facilitate heat transfer from the mounting flange to said portion of the motor housing. There is also an air gap between the heat shield 100 and the motor housing 20. Air from the annulus 76 supercharges this dead-headed air gap. All of these features contribute toward the minimization of heat transfer from the motor housing, via the heat shield, to the air being compressed in the HP compressor.

The present disclosure concerns in particular a number of features that improve the heat transfer from the motor stator 22 and rotor 24 in order to control the temperature of these components. One of these features is the configuration of the liquid coolant passage 25 in the motor housing. With reference to FIG. 1, the motor housing 20 defines an inlet 27 into the coolant passage 25, and an outlet 29 through which the liquid coolant exits the motor housing after having progressed from the inlet 27 and along the coolant passage 25 to the outlet 29. The inlet 27 is proximate the high-pressure compressor side and the outlet 29 is proximate the low-pressure compressor side. As shown in FIG. 1 and further described below in connection with FIGS. 2 through 4, the coolant passage 25 has a generally C-shaped cross-section along a plane generally perpendicular to the direction of liquid coolant flow in the passage. The generally C-shaped passage increases the surface area of the motor housing in contact with the liquid coolant, and thereby enhances heat transfer from the housing into the coolant. It will also be noted from FIG. 1 that the size of the passage cross-section is larger in the portion of the passage proximate the HP compressor, relative to the size of the passage proximate the LP compressor, because the HP compressor has a higher heat load than the LP compressor.

With reference to FIG. 2, a coolant core 125 for use in casting the motor housing 20 is shown in perspective view. Showing the coolant core 125 is a useful way of depicting the configuration of the coolant passage 25 because the passage 25 is a negative of the positive pattern of the coolant core 125. A gravity-pour sand casting process can be used for casting the motor housing 20. Advantageously the motor housing can be formed of an aluminum alloy. The coolant core 125 is made of compacted sand and is easily disintegrated and removed from the cast motor housing after the metal has solidified and cooled. The coolant passage 25 in the cast motor housing comprises a cavity having the shape of the core 125.

As best seen in FIGS. 2 through 4, the coolant core 125 creates a coolant passage having a plurality of axially spaced, convoluted passageways. That is, the coolant passage 25 is not a simple helical passage that coils about the motor housing. Rather, the coolant passage splits into two sets of convoluted passageways each of which routes the liquid coolant through a series of reversals of flow direction about the motor housing axis. Accordingly, the core 125 defines an inlet portion 127 for forming the inlet 27 of the coolant passage, and the inlet portion connects with convoluted portions 130R and 130L. Coolant entering through the inlet 27 splits into two portions, one flowing through the right-hand convolutions (represented by the convoluted portions 130R) and the other flowing through the left-hand convolutions (represented by the convoluted portions 130L). Referring to FIGS. 2-4, arrows are shown to indicate the direction of liquid coolant flow along the coolant passage, which is represented by the positive pattern of the coolant core. The coolant portions rejoin and exit through the outlet, represented by the outlet portion 129.

Additionally, the coolant passage defines at least one bypass passage, and in the illustrated embodiment there are two such bypass passages, which are represented in the coolant core by the tie bars 132 and 134. There is a first set of tie bars 132 located at the top of the coolant core 125 along with the inlet and outlet portions 127, 129, and a second set of tie bars 134 located along the bottom of the core. The tie bars 132 and 134 are connected between adjacent convoluted portions 130 of the coolant core 125 and serve to stabilize the convoluted portions. In addition, the tie bars 132 collectively define a coolant bypass passage in the cast motor housing, and likewise the tie bars 134 collectively define a second bypass passage. Each of the bypass passages intersects the convoluted passageways and extends in a non-convoluted fashion so as to provide alternative flow paths for the coolant to flow between the inlet and the outlet. A particular advantage of the bypass passage at the top, formed by the tie bars 132, is in helping bleed air from the coolant passage 25 during charging of the passage with liquid coolant.

With reference to FIG. 1, a further feature that can be included for facilitating heat transfer away from the motor stator 22 is a heat-conducting material 140 disposed between the stator 22 and the motor housing 20 such that the heat-conducting material is in contact with both the stator and the motor housing. For example, the heat-conducting material 140 can be a heat-conducting epoxy or the like. The heat-conducting material 140 serves as a thermally conductive pathway from the stator 22 to the motor housing 20, which in turn is cooled by the coolant flowing through the coolant passage 25.

While the invention has been described by reference to an electric motor-driven two-stage serial compressor, the invention may also be applied to other electric motor-driven compressors, such as a single-stage compressor. In the appended claims, references to a “first compressor wheel” are to be understood as applying either to the HP compressor wheel of a two-stage serial compressor (in which case the “second compressor wheel” is the LP compressor wheel), or to a compressor wheel in a single-stage compressor.

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 

What is claimed is:
 1. An electric motor-driven compressor comprising: a housing assembly comprising a motor housing and a first compressor housing mounted to one end of the motor housing, the motor housing containing a motor stator and a motor rotor having a shaft, the motor housing defining a bore through which the motor rotor and the shaft pass; the first compressor housing containing a first centrifugal compressor wheel that is mounted on one end of the shaft for rotation therewith, the first compressor housing also defining a first compressor flow path including a first air inlet that leads air into the first compressor wheel, and a first volute that collects compressed air that has passed through and been compressed by the first compressor wheel; and the motor housing defining a convoluted liquid coolant passage therein, the coolant passage defining an inlet and an outlet respectively located proximate opposite ends of the motor housing, the coolant passage defining a plurality of axially spaced-apart, convoluted passageways arranged for serial flow of liquid coolant from the inlet, then through each of the convoluted passageways one after another, and finally out from the outlet.
 2. The electric motor-driven compressor of claim 1, the coolant passage further defining at least a first bypass passage that intersects with the convoluted passageways and extends in a non-convoluted fashion so as to interconnect the convoluted passageways and provide an alternative flow path for some of the liquid coolant from the inlet to the outlet.
 3. The electric motor-driven compressor of claim 2, wherein the coolant passage further defines a second bypass passage that intersects with the convoluted passageways and extends in a non-convoluted fashion so as to interconnect the convoluted passageways, the first and second bypass passages being circumferentially spaced apart from each other.
 4. The electric motor-driven compressor of claim 1, further comprising a second compressor housing mounted to an opposite end of the motor housing and a second centrifugal compressor wheel contained in the second compressor housing and affixed to an opposite end of the shaft, the second compressor housing defining a second compressor flow path including a second air inlet that leads air into the second compressor wheel, and a second volute that collects compressed air that has passed through and been compressed by the second compressor wheel, and further comprising an interstage duct that connects the second volute to the first air inlet such that air compressed by the second compressor wheel is led by the interstage duct from the second volute into the first air inlet and is further compressed by the first compressor wheel and delivered into the first volute, the second compressor wheel thus constituting a low-pressure compressor wheel and the first compressor wheel constituting a high-pressure compressor wheel.
 5. The electric motor-driven compressor of claim 4, wherein the inlet to the coolant passage is proximate the high-pressure compressor wheel and the outlet from the coolant passage is proximate the low-pressure compressor wheel.
 6. The electric motor-driven compressor of claim 4, wherein the convoluted passageway proximate the high-pressure compressor wheel has a larger cross-sectional area than the convoluted passageway proximate the low-pressure compressor wheel.
 7. The electric motor-driven compressor of claim 4, further comprising a heat shield disposed between the motor housing and the first compressor housing, wherein the heat shield defines a mounting flange captured between the motor housing and the first compressor housing, the mounting flange being in contact with a portion of the motor housing cooled by the coolant passage so as to facilitate heat transfer from the mounting flange to said portion of the motor housing.
 8. The electric motor-driven compressor of claim 1, further comprising a heat-conducting material disposed between the motor stator and the motor housing such that the heat-conducting material is in contact with both the motor stator and the motor housing and serves as a thermally conductive pathway from the motor stator to the motor housing.
 9. The electric motor-driven compressor of claim 8, wherein the heat-conducting material is a heat-conducting epoxy. 